For example, Patent Document 1 describes a process for preparing large-size synthetic resin bottles with a handle, such as PET bottles, obtained by fitting a handle to each bottle molded separately. The handle is injection molded and is used as an insert. The handle has a grip, a pair of fitting arms extending frontward from upper and lower ends of the grip, and a stopper disposed at the front of each arm. The handle is fitted to the bottle firmly in the undercut engagement using the stoppers, at the time when the bottle is biaxially drawn and blow molded. This so-called insert molding process is widely in use,    Patent Document 1: JP2001-341745